Vapor recovery system for service stations

ABSTRACT

A vapor recovery system designed for use on underground gasoline storage tanks is disclosed. This design facilitates easy conversion of the present storage tank systems to meet future hydrocarbon air pollution requirements. The vent pipes from each tank are manifolded together underground. A vapor return line connects the manifold to a coupling which is connected to the vapor recovery hose of a tank truck. A vent to the atmosphere is also connected to the manifold.

United States Patent [191 Wagner et al.

[ Oct. 28, 1975 1 VAPOR RECOVERY SYSTEM FOR SERVICE STATIONS [75] Inventors: Walter Wagner, Chaddsford; O. J. Brown, Downingtown, both of Pa.

[73] Assignee: Sun Oil Company of Pennsylvania, Philadelphia, Pa.

[22] Filed: Jan. 2, 1975 [21] Appl. No.: 538,057

[52] US. Cl. 141/1; 141/5; 141/236;

141/285 [51] Int. Cl. B65B 3/04 [58] Field of Search 141/1, 5, 52, 53-61,

[56] References Cited 7 UNITED STATES PATENTS 2,006,393 7/1935 l-lapgood 141/59 UNLEADED GASOLINE I ll ll LJ REGULAR GASOLINE Primary Examinerl-louston S. Bell, Jr. Attorney, Agent, or FirmGeorge L. Church; Donald R. Johnson; William C. Roch 57 ABSTRACT A vapor recovery system designed for use on underground gasoline storage tanks is disclosed. This design facilitates easy conversion of the present storage tank systems to meet future hydrocarbon air pollution requirements. The vent pipes from each tank are manifolded together underground. A vapor return line connects the manifold to a coupling which is connected to the vapor recovery hose of a tank truck. A vent to the atmosphere is also connected to the manifold.

14 Claims, 2 Drawing Figures E PREMIUM GASOLINE 1 U.S. Patent Oct.28, 1975 Sheet 1 of2 3,915,205

U.S. Patent Oct. 28, 1975 Sheet 2 of2 3,915,205

FIGZ.

VAPOR RECOVERY SYSTEM FOR SERVICE STATIONS CROSS REFERENCE TO RELATED APPLICATIONS The vapor recovery system disclosed herein is designed to preferably include float valves such as are disclosed in co-pending application entitled, Float Valve for Use in Vapor Return Lines, Ser. No. 538,053, filed Jan. 2, 1975.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a system for the recovery of hydrocarbon vapors, and more particularly to a system for the collection of hydrocarbon vapors from underground gasoline storage tanks at service stations.

2. Description of the Prior Art The commonly used underground storage system for gasoline consists simply of a plurality of tanks, each having its respective fill tube, gauge line, suction pipe, and vent line. It is also commonly known that a great amount of hydrocarbon vapors escapes from these storage tanks, thereby polluting the surrounding atmosphere. Much of this pollution problem occurs at the time each storage tank is filled. As a result, many systems have been designed to minimize the problem. A secondary consideration has been to isolate the tanks holding different grades of gasoline or unleaded and leaded gasoline. A third consideration is the ease of adding a vapor recovery system to a conventional system. A fourth consideration is the use of the vapor recovery system design on underground storage tanks having remote fill connections.

The vapor recovery system disclosed in Byrd, US. Pat. No. 3,807,433, is relatively simple to convert to, but it has several disadvantages. The main disadvantage is that the vapor must travel through the long vapor return lines, which are usually only 2 inches in diameter, thereby resulting in inefficient vapor recovery due to the pressure drop experienced. Potential contamination problems are also possible.

Several vapor recovery systems are disclosed by the Dover Corporation, OPW Division, 2735 Colerain Avenue, Cincinnati, Ohio, in an advertising booklet entitled, OPW Service Station Vapor Recovery System," published October, 1974. One system, System A-Type l, discloses manifolding the vent pipes together above ground with float valves at the manifold and connecting the vapor return line of the tank truck directly to the manifold. While this system may work satisfactorily in some instances, the problems encountered in the Byrd design will appear in many instances because the length of the vapor flow path is too much. System A-Type 2 discloses the installation of float valves at the location where the vapor line connects to the tank and the connection of the vapor lines into one having the same size as the original vent lines. This system requires excavating to the top of each tank. An additional problem is the use of small vent lines for a plurality of tanks. The above mentioned systems lack the ease of conversion and efficiency needed for vapor recovery systems.

SUMMARY OF THE INVENTION The following vapor recovery system minimizes the problems encountered with the above mentioned systems. For a new underground tank installation, the vent lines for each tank are manifolded together by a manifold having a larger diameter than the vent lines. Valves are placed in each vent pipe at the point where it joins the manifold. A vapor return line connects the manifold to a coupling located near the fill tubes of the tanks. A single vent line to the atmosphere is also connected to the manifold.

For conversion of a conventional storage system to one having vapor recovery capabilities, the existing vent lines from the tanks are interrupted near the tanks and manifolded together as described above for a new underground tank installation. One of the vent lines leading above ground to the atmosphere is connected to the manifold. This method has the advantage over other methods requiring direct access to the tanks. Possible damage to the tank from removing old fittings or from puncture due to excavation, which may require replacement of the tank, is avoided.

Certain design features can be incorporated into the system to give added protection against contamination and for ease of adding vapor recovery lines for vapor recovered from filling automobile gasoline tanks.

Many advantages are gained from this system. By virtue of it being underground, it is essentially tamperproof and less susceptible to accidents. By keeping the length of the vapor return path as short as possible, recovery efficiency is maximized for each system. Location of the fill tubes and vapor recovery connections can be relatively close, thereby avoiding the need for excessive lengths of the vapor recovery hose for each tank truck. I

A better understanding of the invention and its advantages can be seen in the following descriptions of the figures and the preferred embodiment.

DESCRIPTION OF THE DRAWINGS AND PREFERRED EMBODIMENT FIG. 1 shows a schematic view of a vapor recovery system for three underground tanks according to this invention.

FIG. 2 shows an enlarged view of the manifold and its connections.

The schematic diagram shown in FIG. 1 is for illustrative purposes only and is not drawn to scale. The particular relationship of each component to the others will vary in different installations. Three underground gasoline storage tanks are employed in the illustrated examples, each containing a different type of gasoline. For example, tank 11 could contain unleaded gasoline, tank 12 a regular grade of gasoline, and tank 13 a premium grade of gasoline. Each tank ll, 12, and 13 has a fill tube 14, 15, and 16, a gauge line l7, l8, and 19, a suction line 20, 21, and 22, and vent lines 23, 24, and 25, respectively.

In most conventional systems, each vent line runs to a location away from the tanks and vents the vapors straight into the atmosphere. Usually, it is easiest to lay the vent lines in one trench. This fact makes conversion of the conventional system to one having vapor recovery capability a rather simple matter.

The vent lines 23, 24, and 25 are'interrupted at a point close to the tanks where the vent lines are in close proximity to each other. The ends of the vent lines 23, 24, and 25 are connected to a manifold 26 through check valve assemblies 27, 28, and 29, respectively. One of the existing vent lines, 30, that runs above ground to the atmosphere is also coupled to manifold 26. A vapor return line 31 is coupled to manifold 26 and slopes upward to a vapor return dry break coupling 32 secured on its opposite end. The location of coupling 32 is discretionary, but for maximum vapor recovery efficiency this location should be as near to the fill tubes 14, 15, or 16, as possible, so as to minimize the length of the tank truck vapor recovery hose and the length of the vapor flow path. As shown, coupling 32 is shown in a common well with fill tube 14, but this is not essential. The drawing is only schematic and is not intended to represent that fill tube 14 is in fact farther from manifold 26 than the other fill tubes. In this manner, a tank truck operator is assured that if he can reach the fill tubes of the tanks with his delivery hose, he can also reach the vapor recovery coupling with a length of hose no longer than the delivery hose.

The design of the manifold 26 and the couplings therewith is discretionary; however, the design illustrated in the drawings has been proven to operate efficiently. The vent lines from the tanks containing leaded grades of gasoline are connected through the bottom side of manifold 26. The vent lines from the tanks containing unleaded grades are preferably connected through the top side of manifold 26, thereby minimizing the possibility of lead contamination. The atmospheric vent line 30 is coupled to a nipple 33 mounted through the top side of manifold 26, so that any gasoline that might flow into manifold 26 does not block vent line 30. An additional nipple 34 is mounted through the botton side of manifold 26 and capped by cap 34' to provide for an additional tank and its vent line. A third nipple 35 is mounted on the opposite end of manifold 26 from the vapor return line connection and capped by cap 35 for future use. One possible use of nipple 35 is for connection to a vapor return line from a vapor collection system which receives the vapor expelled from an automobile gasoline tank when it is filled. The vapors from an automobile would flow into the manifold .26 and into tanks 11, 12, and 13 through the vent lines 23, 24, and 25.

Various methods of connecting the vent lines 23, 24, and 25 to the manifold are possible. The check valve assemblies 27, 28, and 29 used in the disclosed embodiment are shown in FIG. 2 in more detail. In the check valve assemblies, vent pipes 23, 24, and 25 are connected to valve housings 36, 37, and 38 through reducing couplings 39, 40, and 41, respectively. The valve housings'36, 37, and 38 are each connected to pipe couplings 42, 43, and 44, each of which is connected directly to manifold 26 as shown, except pipe coupling 42. Since vent line 23 is connected to tank 11 which contains unleaded gasoline, its pipe coupling, 42, connects to a 180 pipe elbow 45 which is mounted through the top side of manifold 26, thereby preventing leaded gasoline from entering the unleaded gasoline tank. Valves 46, 47, and 48 are mounted inside valve housings 36, 37, and 38 by connection to couplings 42, 43, and 44, respectively. These valves are designed to prevent gasoline from entering the manifold when the underground tanks are over filled. The valve design disclosed and claimed in the co-pending application is preferable since it will permit high velocity vapor flow without closing, yet close when liquid reaches the valve. This valve will also permit a small amount of gasoline to flow through the valve when it is closed, thereby enabling the tank to receive any gasoline remaining in the hose from the tank truck when the flow is stopped. Also, locating the valve at the manifold eliminates the need of excavating down to each tank for installation or in the event of future maintenance, thereby minimizing the inherent possibility of damaging the tanks and tank fittings.

When a tank truck comes into the service station to fill the underground tanks, it can be stopped at a point where easy access to all connections can be made without using an excessively long vapor recovery hose. The delivery hose (not shown) from the tank truck is connected to the fill tube 14 of the tank to be filled, for example tank II. The vapor recovery hose not shown) from the tank truck is connected to the vapor return coupling 32 of the underground vapor return line 31. When the gasoline flows into tank 11, for instance, the vapors are forced out through vent line 23, through check valve assembly 27, into manifold 26, through vapor return line 31 and into the tank truck through its vapor recovery hose (not shown).

The efficiency with which the vapors can be recovered depends on several factors. The path through which the vapors flow should, preferably, be as short as is reasonably possible. The size of the pipe line through which the vapors flow can be increased in size to increase the capacity of the vapor return lines and the vapor velocity, thereby permitting faster filling of the underground tanks. Use of the proper float valves minimizes the possibility of accidental closing due to vapor velocities and the possibility of wedging the valve closed. Installation of the system underground prevents damage from tampering with this system and from vehicular accidents causing a break in the pipes. Release of vapors into the atmosphere is minimized. Use of an orifice assembly 50 or a pressure/vacuum valve (not shown) on the outside end of vent pipe 30 further reduces the amount of vapors escaping into the atmosphere. Use of the proper pipe sizes will result in vapor pressures that will minimize the vapors forced out of orifice 50 or pressure/vacuum valve.

While a particular embodiment of this invention has been shown and discribed, it is obvious that changes and modifications can be made without departing from the true spirit and scope of the invention. It is the intention of the appended claims to cover all such changes and modifications.

The invention claimed is:

1. In an existing system for underground storage of hydrocarbons comprising a plurality of underground tanks each having a vapor vent line and a fillpipe, each vent line resting in close proximity tofthe other vent lines for part of their underground length, a method for converting the existing underground hydrocarbon storage tank system to one having vapor recovery capabilities with a minimum amount of interference to the existing tanks and comprising:

a. interrupting said vent lines leading from the underground tanks at a common underground location where the vent lines are in close proximity to each other and to the underground tanks, but are not immediately adjacent to the underground tanks, such that the possibility of damage being caused to said underground tanks as well as the possibility of unsettling said underground tanks and causing leaks therein during excavation down to said vent lines at the common underground location are minimized;

b. installing at said underground location a float valve in the interrupted end of each vent line leading to the underground tanks;

c. installing at said underground location a manifold which connects the interrupted ends of the vent lines having the float valves therein; and

d. installing a vapor return line between the manifold and a surface location, such that the installation of the float valves and manifold at the common underground location in close proximity to the underground tanks allows the length of the vapor return path from the tanks, through the manifold, and through the vapor return line to the surface location to be minimized, thereby maximizing the vapor recovery efficiency for each hydrocarbon storage system.

2. Method recited in claim 1, further comprising the step of connecting to the manifold the end of at least one of the existing vent lines leading to the atmosphere, thereby providing a manifold vent line.

3. Method recited in claim 2, further comprising the step of installing on the end of the manifold vent line which remains in the atmosphere a means for restricting the flow of vapor through the manifold vent line, thereby improving the efficiency with which the vapor can be recovered and minimizing the escape of hydrocarbon vapor into the atmosphere.

4. Method recited in claim 3 wherein at least one of the existing underground tanks is utilized to store unleaded gasoline and at least one tank is used to store leaded gasoline, further comprising connecting the interrupted end of each vent line, from an underground tank containing unleaded gasoline and having a float.

valve therein, the upper portion of the manifold, and connecting the interrupted end of each vent line, from an underground tank containing leaded gasoline and having a float valve therein, the lower portion of the manifold.

5. Method recited in claim 4 further comprising the step of providing on the manifold an additional coupling which may be utilized to provide fluid communication between the manifold and a vehicle fuel tank.

6. Method recited in claim 1 wherein at least one of the existing underground tanks is utilized to store unleaded gasoline and at least one tank is used to store leaded gasoline, further comprising connecting the interrupted end of each vent line, from an underground tank containing unleaded gasoling and having a float valve therein, to the upper portion of the manifold, and connecting the interrupted end of each vent line, from an underground tank containing leaded gasoline and having a float valve therein, to the lower portion of the manifold.

7. Method recited in claim 1 further comprising the step of providing on the manifold an additional coupling which may be utilized to provide fluid communication between the manifold and a vehicle fuel tank.

8. A system for the underground storage of hydrocarbons which permits collection of the vapors displaced from the underground tanks when they are being filled and minimization of the vapors escaping into the atmosphere during storage of hydrocarbons and comprising:

a. a plurality of underground tanks'for holding the hydrocarbons;

b. a fillpipe inserted in each tank, through which the hydrocarbons flow into said tank;

. c. a vent line connected to the upper portion of each tank so-that vapors can escape therethrough, each vent line leading to a common underground location in close proximity to the underground. tanks, but; not immediately adjacent to said tanks, such that in the event of excavation at said location, the possibility of damage to the underground tanks and the possibility of unsettling said underground tanks and causing leaks therein are minimized;

d. a manifold connected to said vent lines at said common underground location;

. a valve located in each vent line at the point where each vent line is connected to said manifold; and

f. a vapor return line connected between said manifold and a surface location, such that the length of the vapor return path from the tanks, through the manifold, and through the vapor return line to the surface location, can be minimized, thereby maximizing the vapor recovery efficiency for each hydrocarbon storage system.

9. System recited in claim 8, further comprising:

a. a manifold vent line extending from the manifold to the atmosphere; and

b. means, connected to the end of said manifold vent line, for restricting the flow of vapor through said manifold vent line, thereby improving the efficiency with which the vapor can be recovered and minimizing the escape of hydrocarbon vapor into the atmosphere.

10. System recited in claim 9 wherein at least one of the underground tanks is utilized to store unleaded gasoline and at least one of the remaining tanks is used to store leaded gasoline, further comprising means for connecting each vent line from an underground tank containing unleaded gasoline to the upper portion of said manifold, and means for connecting each vent line from an underground tank containing leaded gasoline to the lower portion of said manifold.

11. System recited in claim 10, further comprising a coupling connected to the manifold which may be utilized to provide fluid communication between the manifold and a vehicle fuel tank.

12. System recited in claim 8 wherein at least one of the underground tanks is utilized to store unleaded gasoline and at leastone of the remaining tanks is used to store leaded gasoline, further comprising means for connecting each vent line from an underground tank containing unleaded gasoline to the upper portion of said manifold, and means for connecting each vent line from an underground tank containing leaded gasoline to the lower portion of said manifold.

13. System recited in claim 8, further comprising a coupling connected to the manifold which may be utilized to provide fluid communication between the manifold and a vehicle fuel tank.

14. In a facility for the storage of hydrocarbons having at least one tank for holding unleaded gasoline and at least one tank for holding leaded gasoline, a manifold system for the vent lines of each tank which is designed to prevent contamination of the unleaded gasoline in each tank containing unleaded gasoline by the leaded gasoline, comprising:

a. an enclosure forming a manifold;

b. at least one coupling connected to the bottom of said enclosure for connection to a vent line from a tank containing leaded gasoline;

flow of gasoline from the tanks through their respective vent lines to said enclosure is restricted; e; a connector connected to the top of said enclosure for connection to a vent line leading to the atmosphere; and

f. a coupling connected to said enclosure for con tion to a vapor return line.

nec- 

1. IN AN EXISTING SYSTEM FOR UNDERGROUND STORAGE OF HYDROCARBONS COMPRISING A PLURAITY OF UNDERGROUND TANKS EACH HAVING A VAPOR VENT LINE AND A FILLPIPE, EACH VENT LINE RESTING IN CLOSE PROXIMITY TO THE OTHER VENT LINES FOR PART OF THEIR UNDERGROUND LENGTH, A METHOD FOR CONVERTING THE EXISTING UNDERGROUND HYDROCARBON STORAGE TANK SYSTEM TO ONE HAVING VAPOR RECOVERY CAPABILITIES WITH A MINIMUM AMOUNT OF INTERFERENCE TO THE EXISTING TANKS AND COMPRISING: A. INTERRUPTING SAID VENT LINES LEADING FROM THE UNDERGROUND TANKS AT A COMMON UNDERRGROUND LOCATION WHERE THE VENT LINES ARE IN CLOSE PROXIMITY TO EACH OTHER AND TO THE UNDERGROUND TANKS, BUT ARE NOT IMMEDIATELY ADJACENT TO THE UNDRERGROUND TANKS, SUCH THAT THE POSSIBILITY OF DAMAGE BEING CAUSED TO SAID UNDERGROUND TANKS AS WELL AS THE POSSIBILITY OF UNSETTLING SAID UNDERGROUND TANKS AND CAUSING LEAKS THEREIN DURING EXCAVATION DOWN TO SAID VENT LINES AT THE COMMON UNDERGROUND LOCATION ARE MINIMIZED, B. INSTALLING AT SAID UNDERGROUND LOCATION A FLOAT VALVE IN THE INTERRUPTED END OF EACH VENT LINE LEADING TO THE UNDERGROUND TANKS, C. INSTALLING AT SAID UNDERGROUND LOCATION A MANIFOLD WHICH CONNECTS THE INTERRUPTED ENDS OF THE VENT LINES HAVING THE FLOAT VALVES THEREIN, AND D. INSTALLING A VAPOR RETURN LINE BETWEEN THE MANIFOLD AND A SURFACE LOCATION, SUCH THAT THE INSTALLATION OF THE FLOAT VALVES AND MANIFOLD AT THE COMMON UNDERGROUND LOCATION IN CLOSE PROXIMITY TO THE UNDERGROUND TANKS ALLOWS THE LENGTH OF THE VAPOR RETURN PATH FROM THE TANKS, THROUGH THE MANIFOLD, AND THROUGH THE VAPOR RETURN LINE TO THE SURFACE LOCATION TO BE MINIMIZED, THEREBY MAXIMIZING THE VAPOR RECOVERY EFFICIENCY FOR EACH HYDROCARBON STORAGE SYSTEM.
 2. Method recited in claim 1, further comprising the step of connecting to the manifold the end of at least one of the existing vent lines leading to the atmosphere, thereby providing a manifold vent line.
 3. Method recited in claim 2, further comprising the step of installing on the end of the manifold vent line which remains in the atmosphere a means for restricting the flow of vapor through the manifold vent line, thereby improving the efficiency with which the vapor can be recovered and minimizing the escape of hydrocarbon vapor into the atmosphere.
 4. Method recited in claim 3 wherein at least one of the existing underground tanks is utilized to store unleaded gasoline and at least one tank is used to store leaded gasoline, further comprising connecting the interrupted end of each vent line, from an underground tank containing unleaded gasoline and having a float valve therein, to the upper portion of the manifold, and connecting the interrupted end of each vent line, from an underground tank containing leaded gasoline and having a float valve therein, the lower portion of the manifold.
 5. Method recited in claim 4 further comprising the step of providing on the manifold an additional coupling which may be utilized to provide fluid communication between the manifold and a vehicle fuel tank.
 6. Method recited in claim 1 wherein at least one of the existing underground tanks is utilized to store unleaded gasoline and at least one tank is used to store leaded gasoline, further comprising connecting the interrupted end of each vent line, from an underground tank containing unleaded gasoline and having a float valve therein, to the upper portion of the manifold, and connecting the interrupted end of each vent line, from an underground tank containing leaded gasoline and having a float valve therein, to the lower portion of the manifold.
 7. Method recited in claim 1 further comprising the step of providing on the manifold an additional coupling which may be utilized to provide fluid communication between the manifold and a vehicle fuel tank.
 8. A system for the underground storage of hydrocarbons which permits collection of the vapors displaced from the underground tanks when they are being filled and minimization of the vapors escaping into the atmosphere during storage of hydrocarbons and comprising: a. a plurality of underground tanks for holding the hydrocarbons; b. a fillpipe inserted in each tank, through which the hydrocarbons flow into said tank; c. a vent line connected to the upper portion of each tank so that vapors can escape therethrough, each vent line leading to a common underground location in close proximity to the underground tanks, but not immediately adjacent to said tanks, such that in the event of excavation at said location, the possibility of damage to the underground tanks and the possibility of unsettling said underground tanks and causing leaks therein are minimized; d. a manifold connected to said vent lines at said common underground location; e. a valve located in each vent line at the point where each vent line is connected to said manifold; and f. a vapor return line connected between said manifold and a surface location, such that the length of the vapor return path from the tanks, through the manifold, and through the vapor return line to the surface location, can be minimized, thereby maximizing the vapor recovery efficiency for each hydrocarbon storage system.
 9. System recited in claim 8, further comprising: a. a manifold vent line extending from the manifold to the atmosphere; and b. means, connected to the end of said manifold vent line, for restricting the flow of vapor through said manifold vent line, thereby improving the efficiency with which the vapor can be recovered and minimizing the escape of hydrocarbon vapor into the atmosphere.
 10. System recited in claim 9 wherein at least one of the underground tanks is utilized to store unleaded gasoline and at least one of the remaining tanks is used to store leaded gasoline, further comprising means for connecting each vent line from an underground tank containing unleaded gasoline to the upper portion of said manifold, and means for connecting each vent line from an underground tank containing leaded gasoline to the lower portion of said manifold.
 11. System recited in claim 10, further comprising a coupling connected to the manifold which may be utilized to provide fluid communication between the manifold and a vehicle fuel tank.
 12. System recited in claim 8 wherein at least one of the underground tanks is utilized to store unleaded gasoline and at least one of the remaining tanks is used to store leaded gasoline, further Comprising means for connecting each vent line from an underground tank containing unleaded gasoline to the upper portion of said manifold, and means for connecting each vent line from an underground tank containing leaded gasoline to the lower portion of said manifold.
 13. System recited in claim 8, further comprising a coupling connected to the manifold which may be utilized to provide fluid communication between the manifold and a vehicle fuel tank.
 14. In a facility for the storage of hydrocarbons having at least one tank for holding unleaded gasoline and at least one tank for holding leaded gasoline, a manifold system for the vent lines of each tank which is designed to prevent contamination of the unleaded gasoline in each tank containing unleaded gasoline by the leaded gasoline, comprising: a. an enclosure forming a manifold; b. at least one coupling connected to the bottom of said enclosure for connection to a vent line from a tank containing leaded gasoline; c. at least one coupling connected to the top of said enclosure for connection to a vent line from a gasoline tank containing unleaded gasoline, thereby assuring that any leaded gasoline which enters said enclosure flows back into a tank containing leaded gasoline and not into a tank containing unleaded gasoline; d. liquid level sensitive valving means mounted for fluid communication with each coupling so that the flow of gasoline from the tanks through their respective vent lines to said enclosure is restricted; e. a connector connected to the top of said enclosure for connection to a vent line leading to the atmosphere; and f. a coupling connected to said enclosure for connection to a vapor return line. 